Electric contact brushes



Oct-24,1967 Q A. D. APPLETON 3,349,210

ELECTRIC CONTACT BRUSHES Filed Aug. 3, 1966 United States Patent 3,349,210 ELECTRIC CONTACT BRUSHES Anthony Derek Appleton, Newcastle-upon-Tyne, England, assignor to International Research & Development Company Limited, Fossway, Newcastle-upon- Tyne, England Filed Aug. 3, 1966, Ser. No. 569,878 Claims priority, application Great Britain, Aug. 6, 1965, 33,850/65 4 Claims. (Cl. 200-166) ABSTRACT OF THE DISCLOSURE An electric contact brush of arcuate form which engages a contact surface at one end of the arc and is mounted at the other end of the are on a spring-biased arm swingable about the center of the arc. The crosssection of the brush preferably tapers outwards from the center to maintain a uniform contact pressure at different radii.

This invention relates to electrical current transfer devices employing solid electrically-conducting brushes.

The most common form of current transfer device in electrical machines is the carbon brush which is normally of rectangular block form and is. supported against the action of a spring in a brush holder.

Conventional brush gear comprising brushes and brush holders requires a certain minimum amount of space which is not always available in some electrical machines such as, for example, homopolar machines, a form of which is described in co-pending application Ser. No. 530,442.

In the aforementioned co-pending application one of the forms of homopolar machine described comprises a disc of electrically conducting material with a coil or coils producing a magnetic field disposed around the periphery of the disc. Current transfer devices are located in contact with the outer rim of the disc near the field coil. In order to make optimum use of the field strength near the field coil, it is necessary to dimension the disc so that its outer periphery is as close as possible to the field coil and this places a limitation on the space available for the current transfer device near the rim of the disc.

The object of the present invention is to provide an electrical current trans-fer device employing solid electrically conducting brushes which is more compact than conventional arrangements.

According to the present invention there is provided an electrical current transfer device comprising a solid electrically-conducting brush biased into engagement with a conducting surface, in which the brush is mounted on a support arm and is biased into engagement with the conducting surface by a torque applied to the support arm.

Preferably the brush is arcuate in shape with one end attached to the support arm and the other engaging the conducting surface. The length of the brush is measured in terms of the angle which the arc subtends, which can be any convenient angle but is preferably 90. The support arm is hinged at its end remote from the end in contact with the brush and a spring force is applied to the arm to cause it to pivot about the hinge and apply a force to the brush and hence to the contact surface.

The cross-section of the brush may be rectangular, square or any convenient shape but in a preferred form the cross-sectional area diminishes with distance from the axis about which the brush pivots so as to maintain a constant contact pressure over the brush cross-section.

The invention will now be described in more detail 3,349,210 Patented Oct. 24, 1967 with the aid of examples illustrated in the accompanying drawings, in which:

FIG. 1 is a side elevation of a current transfer device in accordance with the invention,

FIG. 2 is an end view of the hinged brush forming part of the device of FIG. 1,

FIG. 3 is a perspective view of the brush, and

FIG. 4 shows diagrammatically the application of the device of FIGS. 1 to 3 to a homopolar machine.

Referring first to FIGS. 1 to 3, the current transfer device comprises a solid electrically-conducting brush 1 of arcuate shape subtending an angle of An end face 1a of the brush makes electrical contact with a conducting surface S. The brush has a rectangular protrusion 1b on the other end face to which are riveted two plates 2 which form one leaf of a hinge, being attached to the other leaf 3 at A. The centre of curvature of the brush is coincident with the hinge axis A. A rod 4 is biased against the protrusion 1b by a spring 5 mounted between a collar on the rod 4 and a flange on a sleeve 6 which screws into a bore in a copper plate 7. The force exerted by the spring 5 through the rod 4 on the supporting arm formed by the plates 2 attached to the protrusion 1b tends to swing the brush about the point A and thus biases the contact face 1a into engagement with the surface S. A flexible braid 8 attached to the brush 1 maintains electrical contact with the plate 7.

The biassing force can be adjusted by altering the position of the sleeve 6 and is indicated by the extent to which the rod 4 projects from the sleeve 6. The force alters across the contact face 1a, increasing with distance from the hinge axis A and to maintain a constant contact pressure the area of the face decreases proceeding away from the hinge axis as is shown in FIG. 3. The crosssection shown is trapezoidal, which gives an approximation to uniform contact pressure. If necessary, an absolutely uniform pressure can be attained by using an appropriate cross-section for the brush, but this will not be a simple shape and will present manufacturing dif ficulties.

The arcuate shape of the brush with a uniform crosssection along its length has the advantage that as the brush wears the area of contact remains the same.

The surface S may be the periphery of a slip-ring or commutator. FIG. 4 shows diagrammatically an alternative arrangement for use in a homopolar machine having an electrically-conducting disc 9 rotating within a field coil 10. At the edge of the disc 9 is a projecting rim or flange 11 with the inside of which the brush 1 makes contact.

In the embodiment described the angle subtended by the arc of the brush 1 at the hinge axis A is 90 but this can be changed and may have values up to or more. The brushes can be of commercial brush material such as carbon or a form of carbon such as graphite or graphite with metallic inclusions.

The current transfer device described can be used to collect or supply current to a slip ring, commutator or other contact surface and being compact is suitable for use in any machine where space for such devices is limited.

A further advantage of this invention relates to a situation where a brush is required to operate in a high magnetic field. The reaction between the brush current and the magnetic field produces a force on the brush which would, if located in a conventional brush holder, create serious problems due to a friction force between the brush and its holder. This friction force interferes with the ability of the brush spring to maintain a constant brush contact pressure. This problem is minimised with the brush construction described herein because (a) the brush does not require a holder and the effect of the magnetic force on the brush can be more easily accommodated on the hinge,

(b) the magnitude of the magnetic force is reduced because'of the direction of current flow in the circular brush.

I claim:

1. An electric current transfer device comprising: an electrically-conducting structure having a first contact face; a unitary, solid, electricallyconducting brush of arcuate shape having a uniform cross-section along the length of the arc and a second contact face at one end of said arcuate brush; a hinged supporting arm, said arcuate brush being mounted at its other end on said arm with the center of curvature of the arcuate brush coincident with the hinge axis; and biasing means exerting a torque on said arm to bias said contact faces into engagement, said contact faces lying in radial planes passing through said hinge axis.

2. A current transfer device as claimed in claim 1 References Cited UNITED STATES PATENTS 1,658,677 2/1928 Hanna 200166 1,770,839 7/1930 Carpenter 200166 2,794,888 6/1957 Morse 200--166 2,839,622 6/ 1958 Billings.

ROBERT K. SCHAEFER, Primary Examiner.

H. O. JONES, Assistant Examiner. 

1. AN ELECTRIC CURRENT TRANSFER DEVICE COMPRISING: AN ELECTRICALLY-CONDUCTING STRUCTURE HAVING A FIRST CONTACT FACE; A UNITARY, SOLID, ELECTRICALLY-CONDUCTING BRUSH OF ARCUATE SHAPE HAVING A UNIFORM CROSS-SECTION ALONG THE LENGTH OF THE ARC AND A SECOND CONTACT FACE AT ONE END OF SAID ARCUATE BRUSH; A HINGED SUPPORTING ARM, SAID ARCUATE BRUSH BEING MOUNTED AT ITS OTHER END AN SAID ARM WITH CENTER OF CURVATURE OF THE ARCUATE BRUSH COINCIDENT WITH THE HINGE AXIS; AND BIASING MEANS EXERTING A TORQUE ON SAID ARM TO BIAS SAID CONTACT FACES INTO ENGAGEMENT, SAID CONTACT FACES LYING IN RADIAL PLANES PASSING THROUGH SAID HINGE AXIS. 